title: Circadian rhythm of serum testosterone levels in male beagle dogs--effects of lighting time zone.
abstract: In a previous study, the author found that serum testosterone (T) levels in male beagle dogs showed a circadian rhythm which was lowest at 12:00, and increased to a peak at 18:00-6:00, thereafter decreasing until 12:00. The reason was thought to be that dogs were breeding under rigid controlled conditions. The present study was performed to investigate the effects of lighting on the circadian rhythm of T level by means of a reversal of the lighting time zone, because lighting is considered an important factor in modulating T levels. Six male beagle dogs of 2 years were used in this study. The routine lighting time (8:00-20:00) and dark time (20:00-8:00) zone in the breeding room was reversed completely and T levels were measured at intervals of 1-5 weeks for up to 54 weeks. Blood samples were collected at 6:00, 12:00, 18:00 and 24:00. The results showed that the circadian rhythm of the T level and the T level at each blood sampling time did not change significantly within 54 weeks. As a result, it was recognized that the circadian rhythm of the T level in male dogs may not be affected by changes in the lighting time zone.
authors.affiliation: Division of Comparative Radiotoxicology, National Institute of Radiological Sciences, Chiba-shi, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D004285:Dogs / Q000097:blood / Q000502:physiology*; D008029:Lighting; D008297:Male; D013739:Testosterone / Q000097:blood*; D013995:Time
chemical_list: D013739:Testosterone